netdev - Re: [PATCH net-next-2.6 06/17] sfc: Fix event based MCDI completion and MC REBOOT/CMDDONE ordering issue

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Date:	Fri, 03 Dec 2010 09:09:04 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	bhutchings@...arflare.com
Cc:	netdev@...r.kernel.org, linux-net-drivers@...arflare.com
Subject: Re: [PATCH net-next-2.6 06/17] sfc: Fix event based MCDI
 completion and MC REBOOT/CMDDONE ordering issue

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Thu, 02 Dec 2010 23:46:55 +0000

> From: Steve Hodgson <shodgson@...arflare.com>
> 
> The mcfw *never* sends CMDDONE when rebooting. Changing this so that it always
> sends CMDDONE *before* REBOOT is easy on Siena, but it's not obvious that we
> could guarantee to be able to implement this on future hardware.
> 
> Given this, I'm less convinced that the protocol should be changed.
> 
> To reiterate the failure mode: The driver sees this:
> 
>  issue command
>  receive REBOOT event
> 
> Was that reboot event sent before the command was issued, or in
> response to the command? If the former then there will be a subsequent
> CMDDONE event, if the latter, then there will be no CMDDONE event.
> 
> Options to resolve this are:
> 
>  1. REBOOT always completes an outstanding mcdi request, and we set
>     the credits count to ignore a subsequent CMDDONE event with
>     mismatching seqno.
> 
>  2. REBOOT never completes an outstanding mcdi request. If there is
>     no CMDDONE event then we rely on the mcdi timeout code to complete
>     the outstanding request, incurring a 10s delay.
> 
> I'd argue that (2) is tidier, but that incurring a 10s delay is a little
> needless. Let's go with (1).
> 
> Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>

Applied.
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